The present invention relates to a bus bar of a branch joint box for branching a circuit by connecting thereto connectors of wiring harnesses for a motor vehicle through plug-in means.
Conventionally, in a branch joint box (or junction box) used for joining branches of wiring harnesses for a motor vehicle to various automotive electrical apparatuses, branch joint points are concentrated at one spot so as to joint branches of wiring efficiently and economically. In response to recent trends towards higher density of the wiring harnesses, various types of branch joint boxes are proposed. In the branch joint boxes, a bus bar having tabs used for plug-in connection of connectors of the wiring harnesses is incorporated.
As shown in FIG. 1, a known bus bar 1 of this kind is formed by punching a metal sheet into a preset pattern of a circuit and by providing a number of tabs 1a at predetermined locations of the circuit. When the bus bar 1 is mounted on a substrate, the circuit is cut apart at locations a.
Usually, the known bus bar 1 is produced by punching a sheet of copper or the like. In the case of safety apparatuses mounted on the motor vehicle, for example, a supplemental restraint system (SRS) for supplementing a seat belt, such as an air bag system, two power supply lines, namely, a power source circuit A exclusively used for the SRS and an auxiliary power source circuit B acting also as another circuit are provided.
The power source circuits A and B have two juxtaposed tabs 1b, respectively. Electric current flowing through the tabs 1b from a power source is minute. Thus, in order to improve reliability of connection of the connectors, the tabs 1b are usually plated with metal having excellent electrical conductivity, for example, gold as shown by the crossed hatching. When this gold plating is performed on the tabs 1b, it is necessary to provide the power source circuits A and B at outer peripheral portions of the bus bar 1 and then, form the tabs 1b towards an outer periphery of the bus bar 1 such that the tabs 1b of the power source circuits A and B can be partially plated by hanging the bus bar 1.
However, rack type plating is expensive in which plating is performed by hanging the bus bar 1 one by one. Meanwhile, since circuit configurations of the bus bar 1 are different according to types of motor vehicles, plating facilities are required to be designed exclusively for the types of the motor vehicles, respectively. Furthermore, since the tabs 1b to be plated should be formed towards the outer periphery of the bus bar 1, such problems arise that coupling positions of the connectors are restricted and loss of material of the bus bar 1 is enormous.